MySQL触发器大于条件

Question

Is it possible to create trigger for greater than condition. Suppose I have a column temperature and new values are stored in that column after every 15 seconds. So if the value becomes greater than predefined value(for example 100 degrees) a trigger is generated. Is it possible to do it in mysql?

Answer 1

MySql doesn't implement conditional triggers like Oracle does, for example in Oracle:

CREATE TRIGGER triggername AFTER INSERT ON tablename FOR EACH ROW
WHEN ( condition )
BEGIN 
   ........
END;

the trigger is fired only when condition is meet.

In MySql the trigger is fired every time.
However, it is still possible to use an conditional IF statement inside the trigger and perform some actions only when some condition is meet, for example:

Create table temperature(
  id int primary key auto_increment,
  temperature decimal( 5, 1 )
  );

Create table temp_above_100(
  id int primary key auto_increment,
  temperature decimal( 5, 1 )
  );

CREATE TRIGGER triggername 
AFTER INSERT ON temperature FOR EACH ROW
BEGIN
  IF new.temperature >= 100 THEN
     INSERT INTO temp_above_100( temperature )
     VALUES ( new.temperature );
  END IF;
END;/

INSERT INTO temperature( temperature ) 
VALUES (10), (20), (100), (120 );

click this link: http://www.sqlfiddle.com/#!2/6a930/1 to see results of this example.